Aluminum complex soap greases

ABSTRACT

AN ALUMINUM COMPLEX SOAP GREASE POSSESSING IMPROVED STABILITY IS OBTAINED BY REACTING AN ALUMINUM ALKOXIDE SEQUENTIALLY WITH TWO DIFFERENT CARBOXYLIC ACIDS IN THE PRESENCE OF AN OIL BASE, WHEREIN THE FIRST ACID IS RELATIVELY LESS REACTIVE THAN THE SECOND. AS COMPARED WITH SIMILAR ALUMINUM COMPLEX SOAP GREASES, THIS RESULTING GREASE SHOW SUPERIOR PHYSICAL PROPERTIES, PARTICULARLY IN CERTAIN ROLL TESTS AND WHEEL BEARING PERFORMANCE TESTS, AS WELL AS POSSESSING A HIGHER MELTING POINT.

United States Patent 3,591,505 ALUMINUM COMPLEX SOAP GREASES Arthur T. Polishuk, Media, Pa., assignor to Sun Oil Company, Philadelphia, Pa. No Drawing. Filed June 18, 1968, Ser. No. 737,823 Int. Cl. C10m /14 U.S. Cl. 25237.7 11 Claims ABSTRACT OF THE DISCLOSURE An aluminum complex soap grease possessing improved stability is obtained by reacting an aluminum alkoxide sequentially with two difierent carboxylic acids in the presence of an oil base, wherein the first acid is relatively less reactive than the second. As compared with similar aluminum complex soap greases, this resulting grease shows superior physical properties, particularly in certain roll tests and wheel bearing performance tests, as well as possessing a higher melting point.

BACKGROUND OF THE INVENTION This invention relates to an aluminum complex soap grease and method for preparing the same. More particularly, it relates to an aluminum complex soap grease of improved physical properties which is prepared by certain specific operating conditions described hereinbelow.

The preparation of aluminum complex soap greases and their uses in industrial applications is not new per se. Thus, a detailed description of one such type of material is set forth in U.S. Pats. 2,599,553 and 2,768,138, issued to Hotten et al., wherein an aluminum salt is coprecipitated with an aqueous solution of mixtures of water-soluble soaps to obtain such complex soaps as aluminum benzoate stearate, aluminum toluate stearate, and the like which are then mixed with an oil base,

The preparation of a similar material is described in Bulletin No. 106, and supplement thereof, issued by J. W. Ayers and Co., Easton, Pa., relating to Kolate 40, an alkoxy-substituted cyclic aluminum oxide trimer. As described therein, the cyclic aluminum alkoxide is reacted first with stearic acid in a mineral oil base, and then with benzoic acid, to form the grease of the derivative aluminum benzoate stearate.

The greases produced by the afore-described methods are generally recognized as having higher melting points than conventional greases, and thus are particularly suitable for industrial application in rollers and bearings where high temperatures are frequently found. However, it has been found to be quite diflicult to consistently prepare such greases which are of uniformly high melting point and which also are of high stability in both roller and bearing applications. Often, it has been found that when these greases possess one or two of these qualities in suitable measure, they lack one of the other of such attributes.

It is, therefore, an object of this invention to prepare an aluminum complex soap grease having a high melting point, and which also possesses high stability, particularly in both roller and bearing applications. This and other objects of this invention will be apparent from the ensuing description and claims.

SUMMARY OF THE INVENTION It has now been found, in accordance with the present invention, that when an aluminum alkoxide is reacted sequentially with two different carboxylic acids, wherein the first acid is relatively less reactive with the aluminum alkoxide than is the second acid, the resulting grease not only has a high melting point, but also excellent w CC mechanical stability as shown by certain working, roller and bearing performance tests.

In order to provide a better understanding of the present invention, a description of the chemistry of alumigum soaps as it is presently understood will be provided rst.

By the terms an aluminum complex soap is meant a mixture of aluminum soap molecules containing at least one hydroxyl anion for each aluminum cation and one or more carboxylic acid anions, and preferably two dissimilar acid anions such as one aromatic anion and one aliphatic anion. Thus, it is recognized that all individual soap molecules in a given complex soap are generally not the same. For example, one soap molecule may contain two hydroxyl anions and only one carboxylic acid anion such as an aluminum monostearate; another may contain one hydroxyl anion and two carboxylic acid anions which are the same, as for example, an aluminum dibenzoate or distearate; while yet a third molecule may contain two dissimilar carboxylic acid anions, such as the aforementioned aluminum benzoate stearate. It will thus be recognized that any given aluminum soap preparation will contain a mixture of all three types of molecules, and that the properties of any given aluminum soap preparation will be the average properties of the mixture of molecules present.

While applicant does not wish to be bound by any particular theories, it is believed that the improved properties noted in the aluminum complex soap greases of this invention are due to the presence of a substantial preponderance of soap molecules containing two dissimilar carboxylic acid anions, with only a commensurately small number of monoesters and diesters where both acid anions are the same. The presence of preponderance of molecules containing two dissimilar acid anions is, in turn, believed to be due to the manner in which applicants process is carried out, i.e., by first reacting the aluminum alkoxide with a selected amount of an acid which is the relatively less reactive of the two dissimilar acids selected as the anions of the final soap preparation, thereby producing mostly the aluminum monocarboxylate soap. The subsequent addition of the relatively more reactive acid is then believed to facilitate the introduction of that anion into the partially hindered secondary position of the mono-substituted aluminum alkoxide to produce substantial amounts of the desired di-substituted soap containing two dissimilar anions, By the terms relatively less reactive and relatively more reactive is meant the reactivity inter se of the two acids with respect to the aluminum alkoxide starting material. Included amongst the less reactive acids are, for example, stearic, behenic, myristic, palmitic, and linoleic acids. The more reactive acids includes such compounds as benzoic, alphanaphthoic, beta-naphthoic, acetic and naphthenic acids.

The term dissimilar anions as used hereinabove refers to more than just a mere homologous or like difference between the two anions. For example, for purposes of this invention, pairs of anions such as very short chain (e.g. C -C and long chain (e.g. C -C aliphatic and aromatic; alicyclic and long chain anions and the like are preferred.

Those skilled in the art will recognize from the foregoing description that by the proper selection of two acids of dilferent reactivity, it is possible to form a great variety of aluminum soaps which would be suitable for making greases of improved properties. Other considerations, such as the solubility of the aluminum soap in any given oil will likewise dictate the selection of the acids to be employed. In this regard, see for example the discussion in U.S. Pat. 2,768,138, supra, which is incorporated herein by reference.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The products of the present invention can be conveniently prepared by dissolving an aluminum alkoxide such as aluminum butoxide or aluminum isopropoxide in a small portion of a suitable base oil and heating the mixture to about 100 to 200 F., preferably 150 to 175 F. for a period of from 15 to 30 minutes. The first acid, i.e., the less reactive acid, is then added to the mixture slowly as the alcohol corresponding to the alkoxide anion is evolved and removed from the mixture by evaporation, preferably under vacuum. The temperature is then allowed to increase to within the range of about 175 to 250 F. and preferably from 190 to 220 F. for from 15 minutes to 2 hours. After reaction of the aluminum alkoxide with the first acid is completed, as evidenced by cessation of foaming by the evolved alcohol, the mixture is cooled to about 200 F. and the second acid is then introduced. This may be accomplished by direction addition of the acid to the heated mixture. It is preferred, however, that the second acid be first dissolved in a small portion of the base oil, heated to the temperature of the first mixture, and then added to the first solution. After the resulting alcohol has stopped evolving as indicated by the cessation of foaming, the mixture is then heated to about 380 to 420 F. for about 15 minutes to 2 hours, at which time the balance of the base oil is added and the mixture allowed to cool. Additives, if any, may then be added and the resulting grease may then be milled if desired, although this is not necessary.

An antioxidant is preferably added initially to the base oil in order to prevent oxidation during the heating steps.

While it is preferred that each of the two acids be reacted separately with the aluminum alkoxide, nevertheless, it has further been found that small amounts of the more reactive acid, up to about by weight of the first acid, may be mixed in with said first acid reactant without defeating the purpose of adding the less reactive acid first. Similarly, the more reactive second acid may then contain small amounts, up to about 10%, of the first acid admixed with it.

In an alternate embodiment of this invention, a solvent may be substituted for the base oil during the reactions with each of the two carboxylic acids, in which case the resulting soap is added to the base oil at the completion of the reaction to form the desired grease. Solvents such as petroleum ether, methyl alcohol, water, carbon tetrachloride, etc., may be suitably employed in this embodiment of the invention.

As mentioned hereinabove, the aluminum starting material is preferably a trialkoxide of aluminum wherein the alkyl moiety contains from 2 to 22 carbon atoms. Included amongst the preferred compounds are aluminum butoxide and aluminum isopropoxide, although such compounds as aluminum tallate may also be employed.

As also mentioned above, the acids used to form the aluminum soaps, in addition to possessing relative degrees of reactivity, must all be carboxylic acids, and preferably monocarboxylic acids, although dicarboxylic acids may be employed as well. These acids may be substituted or unsubstituted aliphatic or aromatic carboxylic acids having from 2 to 30 carbon atoms, and preferably 6 to 20 carbon atoms in the aliphatic acids. For purposes of this invention, it is preferred that one of the two acids be an aliphatic acid, preferably stearic acid or palmitic acid, and that the other acid be an aromatic compound such as benzoic acid or u-naphthoic acid. They should, in any event, be dissimilar acids in the manner defined above. Amongst these, the aluminum benzoate stearate soap is most preferred for preparing a grease of high stability.

It is important that the ratios of aluminum alkoxide to total carboxylic acid reactants, and aluminum alkoxide to each respective acid be carefully regulated in order to ultimately obtain a grease of the desired improved stability. It is particularly important, in this regard, that the amount of the first acid which is reacted with the aluminum alkoxide be controlled in order that the formation of the aluminum monocarboxylate soap be maximized and formation of the diester be minimized. While these ratios will naturally vary somewhat depending upon the particular acid or acids employed and their reactivity, the ratio of the less reactive acid to aluminum alkoxide should be in the range of from 0.8 to 1.2 mols of acid to each mol of alkoxide, and preferably a 1:1 ratio, while the ratio of the more reactive acid to aluminum alkoxide is desirably in the range of from 0:8 to 1.2 mols of acid to each mol of alkoxide, and preferably a ratio of 1:1.

While the amount of the second acid need not be controlled as critically as that of the first acid, nevertheless excessive acidity of the final soap should desirably be avoided in order that the soap remain neutral or slightly basic if possible. A number of OH radicals are formed in these reactions. As the number of OH radicals decreases, the soap becomes more acidic and more easily dispersed in mineral oils. As the number of OH radicals increases, the soap becomes more basic and more easily dispersed in polar materials.

When these ratios of starting materials are employed, the ratio of first acid anionzsecond acid anion in the resulting aluminum soap will have a value of from 0.8:1 to 12:1, and preferably 1:1.

Suitable base oils which may be mixed with the aluminum soaps to form the desired greases include lubricating oils of naphthenic base, paraffinic base and mixed base mineral oils and the like, as well as synthetic oils, such as alkylene polymers, polysiloxanes, dicarboxylic acid ester-type oils, or liquid esters of phosphorus acids and the like, such as are described in US. Pat. 2,768,138, supra.

The aluminum soaps are admixed with the base oils in sufiicient amounts to provide a grease of whatever consistency is desired. Generally, soaps in the amounts of 4 to 8% by weight based on the final composition are adequate for NLGI #2 grade greases, and preferably from 4.5 to 6.5%, although none of these amounts is particularly critical.

Various additives may be introduced into the final composition if desired, as for example, oxidation inhibitors, dyes, fillers, anti-corrosive agents, extreme pressure agents such as conventional mixtures of lead naphthenate and sperm oil and the like. Particularly useful are antioxidants such as phenyl alpha-naphthylamine which are preferably added to the base oil prior to admixing it with the reactants at elevated temperatures.

The improved properties of applicants novel grease composition are best described and understood with reference to the following examples, wherein the properties of said grease are compared with those obtained by methods generally known in the art. The extreme pressure agent used in each example was a commercially available mixture of lead naphthenate and sperm oil.

Example 1 The following ingredients were used:

Soap: Weight percent Stearic acid 4.3 Benzoic acid 2.1 Aluminum isopropoxide 3.2 Water 0.3

Base Oils:

Parafiinic, SUS/2l0 F. 77.8 Naphthenic, SUS/210 F. 8.3

Additives:

Extreme pressure agent 3.5 Phenyl alpha-naphthylamine 0.5

Total 100,0

In the preparation of a grease utilizing the above materials, the aluminum isopropoxide was dissolved in about one-third of the mixed base oils and heated to 250 F. The stearic acid was added slowly with stirring. Foaming indicated the release of isopropyl alcohol. The temperature dropped during this period to between 210 to 220 F. due to the heat of evaporation. After the foaming had ceased, the benzoic acid was introduced. This was accomplished by dissolving the benzoic acid in about onethird of the base oil, heating the mixture to between 200 to 220 F. and introducing this solution into the first solution while stirring.

Additional foaming indicated the further evolution of isopropyl alcohol. When this reaction was completed, the mixture was cooled to 200 F. and the water was added. After 20 minutes of stirring at 200 F., the mixture was heated with stirring to 400 F. at which time the remainder of the base oil was added and the mixture allowed to cool to 180 F. The additives were then introduced and the composition milled lightly.

Example 2 In another preparation of the same type of grease using the same materials as in Example 1, the aluminum isopropoxide, stearic acid, phenyl alpha-naphthylamine and benzoic acid were added together to about two-thirds of the total oil at room temperature. The mixture was heated slowly with stirring to 200 to 250 F. After all of the isopropyl alcohol was evolved, the mixture was cooled to 200 F., water added, stirred for 20 minutes and slowly heated to 400 F. It was then cooled and the remaining oil added. When the grease temperature fell below 200 F., the extreme pressure agent was added and the grease milled lightly.

Example 3 In a third preparation of the same type of grease as was prepared in Examples 1 and 2, but substituting the cyclic trimer or aluminum isopropoxide for aluminum isopropoxide, the following materials were employed:

The stearic acid and phenyl alpha-naphthylamine were added to one-third of the base oil and heated to 180 F. with stirring. When the ingredients were completely dissolved the cyclic trimer was added and heated to 220 F. After the evolved alcohol and esters were removed, the benzoic acid, dissolved in one-third of the base oil at 200 F., was added slowly with stirring. Further evolution of alcohol, water and esters occurred. After this evolution, the mixture was heated to 400 F. The heat was removed and the final one-third of the oil added. When the temperature of the mixture became less than 200 F., the extreme pressure agent was added and the grease was milled lightly.

It will be noted that the grease composition of Example 1 was prepared in accordance with the process described herein'above. The grease composition of Example 2 employed the same ingredients, but in accordance with this method both of the acids were reacted with the aluminum alkoxide simultaneously. The grease composition of Example 3, on the other hand, was prepared by sequentially reacting a closely related aluminum compound; i.e., the cyclic trimer of aluminum isopropoxide, first with stearic acid, and then benzoic acid.

Each of these grease compositions was then subjected to a series of standard tests, the results of which are reported in Table 1, below.

Data in Table 1 shows that the products prepared by the method of Example 2 possess good characteristics, as shown by the R011 Stability Test, but poor properties as evidenced by the Wheel Bearing Leakage Test. The reverse is true of the products of Example 3, wherein the R011 Stability Test results are poor while the Wheel Bearing Leakage Test results are good. Unexpectedly, however, the grease composition prepared by the process of this inven tion possesses outstanding characteristics in both respects. Moreover, these improvements are accomplished by an improvement in the Dropping Point of the grease, as compared with the other two products, and a high level of mechanical stability, as shown by the results of the penetration tests, after working in the Grease Worker as much as 10,000 strokes or more.

What is claimed is: Y

1. A grease composition comprising a major proportion of a lubricating oil and, in an amount suflicient to form a grease, an aluminum complex soap having two structurally dissimilar carboxylic acid anions, said soap being formed by reacting an aluminum alkoxide having from 2 to 22 carbon atoms in each alkyl group sequentially with two carboxylic acids of different reactivity rates with respect to said aluminum alkoxide, wherein a carboxylic acid of lesser reactivity selected from the group consisting of higher fatty acids and aliphatic dicarboxylic acids having at least 10 carbon atoms is first contacted with the aluminum alkoxide until the reaction is complete, followed by contact of said alkoxide with a carboxylic acid of greater reactivity selected from the group consisting of lower fatty acids, aliphatic dicarboxylic acids having less than 10 carbon atoms, and aromatic monocyclic and dicyclic monocarboxylic and dicarboxylic acids, wherein further the ratio of the carboxylic acid anion of lesser reactivity to the carboxylic acid anion of greater reactivity in the resulting aluminum soap has a value of from 0.8:1 to 1.221.

2. The composition according to claim 1 wherein at least one of said acids is a higher fatty acid.

3. The composition according to claim 1 wherein the less reactive acid is stearic acid and the more reactive acid is benzoic acid, whereby the resulting aluminum complex soap is an aluminum benzoate stearate.

4. The composition according to claim 3 which is further characterized in that the resulting grease has a Dropping Point above 500 F., a Roll Stability percentage change of less than 10 and a Wheel Bearing Leakage of less than 10 grams.

5. A method of preparing an aluminum soap grease which comprises dissolving a solution of aluminum alkoxide, wherein each alkyl group contains from 2 to 22 carbon atoms, in a first portion of lubricating oil at elecated temperatures, adding a sufiicient amount of a first carboxylic acid selected from the group consisting of higher fatty acids and aliphatic dicarboxylic acids having at least 10 carbon atoms to said solution to form an aluminum monocarboxylate soap and release alcohol, thereafter adding a second carboxylic acid selected from the group consisting of lower fatty acids, aliphatic dicarboxylic acids having less than 10 carbon atoms, and aromatic monocyclic and dicyclic monocarboxylic and dicarboxylic acids to said solution at elevated temperatures to form an aluminum dicarboxylate soap and release additional alcohol, thereafter cooling the mixture, adding water and then reheating the mixture while adding sufiicient additional lubricating oil to said solution to thicken said solution to a gel-like consistency, wherein the reactivity rate of the first acid with respect to the aluminum alkoxide is less than that of the second acid, and wherein further the mol ratio of the first acid to the aluminum alkoxide and the mol ratio of the second acid to the aluminum alkoxide in the resulting soap is in the range of from 0.8: 1 to 1.2: l.

6. The process according to claim 5 wherein at least one of said acids is a higher fatty acid.

7. The process according to claim 5 wherein the first carboxylic acid contains not more than 10 weight percent of the second carboxylic acid admixed with it.

8. The process according to claim 5 wherein the second carboxylic acid contains not more than 10 weight percent of the first carboxylic acid admixed with it.

9. The process according to claim 5 wherein the second carboxylic acid is added to the solution dissolved in a second portion of lubricating oil.

10. The process according to claim 5 wherein the first acid is stearic acid and the second acid is benzoic acid.

11. The process according to claim 5 wherein the aluminum alkoxide is aluminum isopropoxide.

References Cited UNITED STATES PATENTS 2,469,041 5/1949 Jones 252-35 2,768,138 10/1956 Hotten et al 25237.7

DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner US. Cl. X.R. 252-35 

